I'm in Alberta, the province that produces most of Canada's oil, and there's only one question on everybody's lips. How long will the oil price stay down? It has fallen by more than half in the past nine months — West Texas Intermediate was $48 per barrel this week — and further falls are predicted for the coming weeks.

This hits jobs and government revenues hard in big oil-producing centers like Alberta, Texas and the British North Sea, but its effects reach farther. "Clean" energy producers are seeing demand for their solar panels and windmills drop as oil gets more competitive. Electric cars, which were expected to make a major market breakthrough this year, are losing out to traditional gas-guzzlers that are now cheap to run again.

Countries that have become too dependent on oil revenues are in deep trouble, like Russia (where the ruble has lost half its value in six months) and Venezuela. Countries like India, which imports most of its oil, are getting a big economic boost from the lower oil price. So how long this goes on matters to a great many people.